This invention concerns a gear checking machine which is particularly useful in measuring helical lead and involute gears, especially large gears those on the order of 40 to 60 inches or more in diameter. The measurement of the helical lead and of the involute both require an accurate timed relationship between a rotating axis and linearly driven test probe. Prior art involute checkers utilize a ratio bar in conjunction with a master base circle sector or disc. This type of machine had physical limitations which placed severe limitations on the accuracy of the machine and the configuration of the gear support table in the measurement of large gears on the order of 40 to 60 inches or more in diameter. The timed relationship between a rotating axis and linear motion of the helical lead testing machines of the prior art is generally accomplished by a sine bar unit which transmits an accurate angular measurement. Machines incorporating these device are to be seen in U.S. Pat. Nos. 2,787,060 and 2,998,657.
The present invention eliminates the ratio bar and sine bar and utilizes a large disc or base circle which is coupled to the gear support table. The large base circle is operatively attached to an encoder which accurately registers by electronic pulses the angular or rotary movement of the base disc. The input of this encoder advantageously is achieved by utilizing a very small diameter disc which is normally driven by the outer periphery of the large base disc. This large ratio between the base disc and the encoder disc provides a large range of accuracy in determining the angular movement of the disc.
Two simple discs with properly calculated diameters rotating with each other can provide a much wider range of ratio and accuracy than that obtainable by another device.
A number of advantages are gained by this device in proportioning, manufacturing and in assembly. These are:
1. Flexibility-- large ratio range can be obtained.
2. Changes can be readily made by changing diameter of mating disc.
3. Round configuration-- easy to make-- easy to manufacture.
4. Exact ratio can be obtained by simple regrinding of the smaller disc.
5. Positive drive can be obtained by holding the discs in contact by means of springs, adjustable pressure bar, weights, etc.
In summary, incorporation of base disc principle in conjunction with stepping motors and gear boxes, provides a wide range of proportioning at a very low cost not possible with other known methods.
It is therefore an object of the present invention to provide a gear checking machine having a rotatable table for supporting a gear to be checked which is coupled through a shaft to a large diameter base disc which is frictionally driven by a small diameter wheel that is in engagement with the periphery of the large base disc wherein the large base disc in turn frictionally drives a small wheel which is coupled to a position indicating encoder.
It is an additional object of the present invention to provide a gear checking machine which has a rotatable table for supporting a gear to be checked wherein the table is coupled to a large diameter base disc having a circular cross-sectional configuration, the periphery of which is utilized to drive a disc of a predetermined diameter which is substantially smaller than the diameter of the base disc and which is coupled to an encoder to provide a signal which is indicative of the degree of rotation of the support table.
It is a further object of the present invention to provide a drive and encoding system for a gear checking machine in which a table for supporting the gear to be checked may be driven at a rate which may be easily varied by changing the diameter of a small drive wheel that it utilized to frictionally drive a large base disc which is coupled to the rotatable table and the resolution of the encoder, which emits signals which are representative of the rotation of the table, may be easily varied by changing the diameter of a small wheel which is frictionally driven by the large diameter base disc.
Other objects and advantages of the present invention will be apparent to those skilled in the art from the disclosure of this invention.